The Problem with Dams

If You Build Them, They Will Come

Nov. 9, 2017

Some two months after the flood, neighborhoods on upper Buffalo Bayou were still haunted. A moldy, gray pall hung in the air like the Spanish moss draped in the trees. Houses were empty, their windows dark, walls stained where the dark floodwaters rose. Lawns and gardens were ruined, muddy and brown. Scattered piles of debris, broken mirrors and plasterboard, lined the nearly lifeless streets. The air, even out of doors, smelled of mildew.

“They’re having a hard time being more …. positive,” said resident Michelle Foss, her voice trailing off, looking towards a house where a family with children had to be rescued by helicopter from the roof.

Halloween decorations in front of a home in Briargrove Park on Buffalo Bayou that flooded during Hurricane Harvey. Photo by SC Oct. 20, 2017

Foss’s neighborhood is Briargrove Park. Like most of the subdivisions along Buffalo Bayou, it was developed in the decades after the federal government built two earthen dams west of Houston on what was then, in the late 1940s, mostly prairie—ranch and farmland. But the land next to the ancient meandering river, in the natural floodplain, was graced with forests of tall oaks and other trees—ideal for upscale residential development. With the construction of the dams, the floodplains were now considered safe. During heavy rains, the reservoirs behind the dams, Addicks and Barker, would hold back the waters of Buffalo Bayou, Houston’s main river, its Mother Bayou, and several creeks flowing into it, until the rain runoff collected in the bayou below the dams could empty into Galveston Bay.

It was a classic case of moral hazard, a situation identified by the late renowned geographer Gilbert White as early as 1942 in a paper titled, “Human Adjustment to Floods.” Government sponsorship of structural solutions like levees and dams that protect floodplains encourage development in those floodplains, which leads to damages that are often worse than what would have happened prior to construction of the levees and dams. (pp. 17-18) (See also p. 2.)

In the wake of Hurricane Harvey, the calls for a new or third reservoir in west Houston are virtually unanimous.  It’s worth considering whether that might be a mistake.

 

A False Sense of Security

A house that flooded next to Buffalo Bayou in Briargrove Park during Hurricane Harvey. Photo by SC on Oct. 20, 2017

For decades the scenic suburban neighborhoods in the bayou’s sloping floodplain forests remained safe and prosperous. More subdivisions, roads, schools, churches, and shopping centers were built, including upstream of the reservoirs, even literally in the reservoir flood pools. The two dams were designed originally with five outlets, four of them ungated, allowing for a combined discharge of 15,700 cubic feet per second (cfs) into the bayou, including the flow from rain runoff below the dams, as measured by the USGS gauge at Piney Point. Interestingly, this original planned rate of flow is about what would be released into the bayou during Harvey some 75 years later, when the US Army Corps of Engineers was forced for the first time to open the floodgates during a storm. The difficult decision—it was known that flooding would result—was made to protect the aging dams from being overwhelmed by an unprecedented amount of rain rapidly running off the developed land upstream. Three people died downstream and thousands of homes, businesses, and cars were flooded both below and above the reservoirs.

By the time construction of the dams was completed in 1948, however, two of those four uncontrolled outlets were gated, reducing by half the maximum free flow of the bayou and its tributaries through the dams to 7,900 cfs during a storm. Then, with more development along the bayou, the threat of flooding that development increased, and in 1963 the Corps decided to gate the remaining two outlets. Maximum flow was cut to 2,000 cfs, a quarter of the previous limit. (p. 12)

But after some sixty years of operation, the earthen dams had alarming seepage problems and voids. Adding to the pressure, development upstream of the dams had increased runoff into the reservoirs. Operations and maintenance costs, not including repairs, had tripled from about $900,00 in 1972 (p. 15-14) to about $3 million annually in today’s dollars (p. 36). In 2008 the Corps began $4.4 million in “interim risk reduction measures.” Concerned about the risk of catastrophic failure, in 2010 the Corps decided to reverse course and double the maximum release rate, including the downstream flow, to 4,000 cfs, in order to reduce pressure from high water levels in the pools behind the troubled dams. (p. 2) Flows any higher than that were now problematic. The Corps found that because of ever increasing development in the floodplain, flows at or above 4,100 cfs would flood the lower levels of homes built along the bayou from North Wilcrest to Chimney Rock Road, sixteen miles downstream. (p. 3)

In recent years, however, not even the dams could prevent homes from flooding along the bayou. Because of the rapid rate of rainwater runoff from our paved and built city, the flow in Buffalo Bayou can greatly exceed 4,100 cfs during a storm when the dam floodgates are closed. In 2015, during the Memorial Day flood, the flow exceeded 8,500 cfs, and again in 2016, flow was greater than 7,000. Residences up and down the bayou flooded during both events, including in Foss’s Briargrove Park neighborhood on the south bank, even with the floodgates closed.

 

And Then Came Harvey

The rain from Hurricane Harvey started Friday, Aug. 25, slowly at first. The dam floodgates were closed. Work on the new floodgates, a $72 million project finally begun in the spring of 2016, was suspended. By Sunday morning the flow in Buffalo Bayou was well over 10,000 cfs and houses near the bayou were flooding, though often first from the overflowing streets as drainage systems designed to empty into the bayou backed up and even reversed from the pressure of the swollen river.

Flooding in the street had trapped retired corporate attorney Landrum Wise in his house along with his wife and cats and a neighboring family with small children who had taken refuge on the second floor. The Wise house is one of the few two-story structures in Walnut Bend, a subdivision of ranch-style homes on the south bank of the bayou just west of Beltway 8 developed after construction of the dams. The backyard backs up to the woods of Terry Hershey Park, a 6.2-mile long stretch of the bayou immediately below the dams that was rerouted, stripped, and straightened by the Corps of Engineers in the late 1940s. The project cut off numerous meanders, many of them now remnant oxbow lakes. Channelizing, straightening, and concreting streams is now an outdated and largely abandoned practice. Flushing stormwater downstream as rapidly as possible, it was discovered, not only caused more flooding and erosion downstream but also disrupted the stream’s natural process, killing vital organisms and sending polluted water into our bays.

With the gating of the dams and restriction of the flow in the Sixties, funneling water downstream as fast as possible was thought to be less important. The stripped and straightened stretch, about 500 acres, was allowed to return to nature. The land was sold to the Harris County Flood Control District, which in the 1990s removed trees on the north bank and created a 100-acre-foot stormwater detention basin to hold overflow from the bayou during heavy rains. The area became a county park in 1993, named after the environmentalist, Terry Hershey, who in the mid-Sixties, together with other homeowners on the bayou, stopped the Corps from stripping, channelizing and concreting the entire length of the bayou from Beltway 8 to Shepherd Drive.

But the flood control district, as well as the City of Houston, continued with plans to remove more trees and build detention basins along the artificial channel in Hershey Park, despite the fact that trees and vegetation are powerful natural stormwater detention devices, critical for slowing runoff—increasing the lag time—and reducing peak flow in a flooding stream. Wise and many of his neighbors, including retired chemical engineer Michael Huffmaster, opposed the detention plans. The amount of detention to be created was “trivial,” said Huffmaster, standing recently behind his flooded house on a remnant oxbow of the bayou in the Lakeforest subdivision upstream from Wise and just downstream from North Wilcrest. “We need like 2,000-acre-feet,” he said. Their group, called Save Our Forest, advocated placing the detention basins on undeveloped private land and identified several alternative locations, said Huffmaster, who is also president of the Briar Forest Super Neighborhood, a group that includes many of the neighborhoods on the south side of the bayou near Terry Hershey Park as well as Foss’s neighborhood east of Beltway 8.

 

Michael Huffmaster, president of the Briar Forest Super Neighborhood, behind his flooded house on a remnant meander of Buffalo Bayou in the Lakeside Forest subdivision. Photo by SC Oct. 20, 2017

Alas, our state and local revenue system is built on sales and property taxes, and the need for property tax revenue in particular influences political decisions on everything related to development and flood management. Parks, green space, detention basins, buyouts remove land from the revenue stream; big dam and drainage projects spread public money around and theoretically protect flood-prone land for development. Building detention on public park land, which already produces no property tax revenue, is cheaper than having to buy private land which if developed would be a source of tax revenue.

At a standing-room-only meeting last month of the Briar Forest Super Neighborhood, the flood control district’s director of operations, Matt Zeve, was jeered by flooded property owners when he announced that the district would be reviving the detention basin plan, beginning with a vegetation survey, and terminating leases of flood control district property to homeowners on the edge of the park.

“What is that going to do for us?” angrily cried one flooded resident.

 

The Floodgates Open

Late on Sunday, Aug. 27, in the middle of the night and in the early hours of the next morning, the Corps of Engineers opened the floodgates on the reservoirs for the first time during a storm. Water was rising rapidly behind the 70-year-old earthen dams, and would likely soon flow around the spillways at the ends of the dams, also for the first time.

Buffalo Bayou was already flowing at over 10,000 cubic feet per second (Piney Point gauge), more than double the level for flooding property along the bayou. It was still raining and had been raining for three days. Hurricane Harvey had dropped some 10-17 inches of rain on the west side of town, though on the east side of the Harris County the rainfall was nearly double. The rain wouldn’t stop until Aug. 29, two days later, ultimately deluging the region with more rain than had ever been recorded in the United States: nearly 65 inches on Nederland near Beaumont, with some 56 inches on southeast Houston, and 30-40 inches falling all over the county.

The floodgates on the dams were opened slowly at first. Huffmaster thought he was prepared. He researched the rainfall and how high the bayou would rise if the Corps released as much as 8,000 cfs from the two dams into the already flooded bayou. Downstream in Michelle Foss’s neighborhood of Briargrove Park, a resident made the same calculation. There the bayou would rise to about 71 feet. Street level was about 60 feet. (In fact, the neighborhood was even lower than people realized. The neighborhood had subsided about one foot since the late 1990s.) Massive flooding. An email warning went out to Foss, an energy economist, and her neighbors, many of them engineers, geologists, economists, accountants, and other professionals, “a data-driven group,” said Foss. Nobody believed the warning. “We thought, ‘This can’t be true.’” Only that one man who sent out the warning packed up and left.

Huffmaster and his wife ended up wading through chest-deep water to escape their flooding home, “our wonderful tree house.” Wise and everyone on his street were rescued by firefighters on rubber rafts, Jet Skis, and kayaks.

Harris County Flood Control District projection of flooding along Buffalo Bayou on Aug. 29, 2017, following release of stormwater from the federal dams.

 

Responses, Solutions, Priorities: Buyouts, A New Reservoir on The Prairie, Widening and Straightening.

As in many neighborhoods up and down the bayou and around the city, the talk on the street in Briargrove Park is of what to do, who is staying, who is rebuilding, who hopes to be bought out and leave, how the neighborhood will survive as a neighborhood.

Foss and her husband have lived in Briargrove Park since 1985. They are repairing their architect-designed home, built in 1960 and flooded for the first time during Harvey. Foss and some of her neighbors have also taken the initiative to research the topography and history of their neighborhood and come up with a plan to save it. After the flooding in 2015, residents had formed a Committee on Stormwater Drainage and Water Quality as part of their Homeowners Association. Longtime residents believe that a corner of the neighborhood had once had a swale or ravine that drained into the bayou. But the homeowners’ association had sold the land. The swale was filled and a house built on top. The house now floods, and the lack of drainage is causing other houses in the neighborhood to flood. The owner is ready to sell, and Foss’s committee is forming a nonprofit to raise money, both private and public, buy the house, restore the swale, and put the land into a trust or conservation easement as greenspace so that the streets can drain.

Michelle Foss in the backyard of a house built on a filled ravine in the Briargrove Park neighborhood on the south bank of Buffalo Bayou east of Beltway 8. Foss and her neighborhood committee are raising money to buy this house and restore the ravine for drainage and protection of other houses. Photo by SC Oct. 20, 2017

Foss calls it a “strategic buyout.” This home, valued at $750,000, and others in the neighborhood, are probably too expensive for the county to purchase as part of a government-funded buyout program. With politicians prioritizing big, expensive engineering projects, there isn’t enough money to go around anyway. But Foss has spoken with local political representatives and hopes her group can get some public support and possibly serve as a model. “I’m betting there are fifty neighborhoods with drainage like this,” she said.

For his part, Huffmaster is focused on taking the “kinks” out of the bayou. The “tortuous twists,” as he describes the bayou’s characteristic meanders, are stopping the flow, he says, causing the water to back up into the straightened stretch upstream and into his house. Theoretically, it should happen differently. The straightened stretch should send water shooting downstream and over the bank where it hits a meander. And in fact it does do that.

Downstream from Huffmaster and the straightened stretch of Hershey Park, the first big meander or “kink” east of the beltway flows around the cul-de-sac of Legend Lane on the north bank. The houses there flood badly. But Foss has a solution: another strategic buyout. She thinks the flood control district should buy and tear down the houses there. The bayou wants to cut straight across the point on which the houses are built. It should be allowed to do that naturally, said Foss.

“Messing around with the channel is only going to create more problems,” she said. “Figure out where river wants to go and take advantage of it.”

 

  • Street in Briargrove Park two months after flooding from Buffalo Bayou and Hurricane Harvey. Photo Oct. 20, 2017
  • Map of ponding in Briargrove Park caused by house built on filled ravine. Neighborhood flood committee wants this house and another further north purchased and removed for drainage. Image City of Houston, 2017
  • Map showing flooded Legend Lane properties on north bank of Buffalo Bayou meander recommended for strategic buyout along with homes on south bank in Briargrove Park. Aerial image Aug. 30, 2017.
  • Lidar image showing elevations along Buffalo Bayou west and east of Beltway 8. Blue is lowest, red is highest. Courtesy Michelle Foss

 

But Huffmaster is not alone in calling for “improvements” to the channel of Buffalo and other bayous and streams. Virtually every politician, engineering and developer group has listed enlarging channels or increasing conveyance in our waterways as a top priority, which is a lot like calling for bigger highways to deal with traffic congestion:  it doesn’t work.  Flooding begins on the land, and managing flooding in place, stopping raindrops where they fall, is the modern approach to reducing urban flooding.

In Buffalo Bayou in particular, “improving” the channel is also impractical and prohibitively expensive. At that recent Briar Forest Super Neighborhood meeting, Flood Control Operations Director Zeve explained why: most of the land is privately owned. And under current federal law, altering a stream like Buffalo Bayou requires replacing or “mitigating” the loss of ecological function by creating riparian wetland elsewhere.

 

The Third Reservoir: Who Benefits?

Also at the top of politicians’ flooding To Do list is The Third Reservoir. Virtually everyone is calling for a Third Reservoir, other than a handful of environmentalists and academics. It even has a price tag already: $400 million.

But what is this Third Reservoir? Where would it be? And what are its benefits?

“We have no details about the third reservoir,” says Mary Anne Piacentini, executive director of the Katy Prairie Conservancy. “So it’s hard to know exactly how to respond.”

“It’s fuzzy,” says Evelyn Merz of the Houston Sierra Club. “What exactly do they mean by a third reservoir? Is it a big hole in the ground, a traditional reservoir like Addicks and Barker? Or is the idea to have open space that can function as prairie and hold and retard runoff?”

The Third Reservoir appears to be a version of a plan developed by the Harris County Flood Control District known as Plan 5 (see p. 104), though Piacentini says the current idea is “most likely different.” Plan 5 is a variation of a levee in northwest Harris County that was proposed by the Corps of Engineers in 1940. The levee, as well as subsequent plans, was intended to capture the flooding from Cypress Creek that flows across the Katy Prairie into the Buffalo Bayou watershed and Addicks and Barker reservoirs. Development in the floodplain of Cypress Creek has exacerbated that flooding across the prairie, which is itself under heavy development pressure, particularly since the construction of the controversial Grand Parkway. (See also here and here and here.)

Generally, all parties agree that Addicks Reservoir in particular cannot handle more rain runoff. (Both reservoirs are for flood-control only, usually dry, and contain recreational facilities, even a zoo.) During Harvey, for the first time ever, storm water impounded behind Addicks, which is immediately north of Interstate 10, flowed over an emergency concrete spillway at the north end of its 11.7-mile long dam. Addicks can store about 130,00 acre-feet of water before the open-ended pool backs up and inundates subdivisions behind government-owned land to the north and west. Total capacity is about 200,00 acre-feet before the water begins flowing around the spillways, an elevation of 108 feet (above mean sea level). During Harvey, on August 30, the water level peaked at 109.1 feet, a record.

In a 2015 study, the flood control district estimated that during a so-called 100-year flood (pretty big rain, previously your maximum planned-for flood but lately a relatively piddling event), about 23,355 acre-feet of water flows from Cypress Creek across some 21,000 acres of largely undeveloped (mostly agricultural) prairie (p. 9) surrounding the Grand Parkway and into the streams feeding Addicks Reservoir (p. 179). (Harvey was way bigger than that – an unprecedented 1,000-year flood. The Memorial Day and Tax Day floods of 2015 and 2016 too were bigger, 500-year events though more localized.)

Apparently during the Tax Day 2016 rains, which landed heavily on northwest Harris County, it took about 24 to 30 hours for the Cypress Creek overflow to make its way into Addicks Reservoir once the storm had started, according to a 2016 analysis by HCFCD meteorologist Jeff Lindner. (p. 28)

The idea is to construct some sort of berm that would hold back this runoff even longer and protect for future development much if not most of those 21,000 acres served by the Grand Parkway  (p. 17), perhaps reserving some 5,000-6,000 acres as prairie. (p. 9) Development of the land, of course, could in turn cause greater, faster runoff that would have to be handled somehow. Another key question is how long the prairie behind the berm or dam would be submerged. Wetlands can hold water indefinitely, points out Piacentini, but prairie grasses cannot.

  • Aerial view of the Grand Parkway (99) with Cypress Creek the dark green band across the top and Addicks Reservoir the dark green space in the bottom right. Proposed third reservoir would go somewhere south of the creek to protect for development land now occasionally inundated by the creek. Image apparently a combination of an image shot on Feb. 24, 2017, west of the parkway and Aug. 30, 2017, to the east.
  • The 1940 federal flood control plan for Houston including a levee below Cypress Creek on the prairie northwest of the city. Image courtesy of US Army Corps of Engineers
  • A map showing the land protected by the Katy Prairie Conservancy (green) and developed (non-agricultural) land (gray). Image courtesy of the Katy Prairie Conservancy.
  • A 2015 image of the proposal by the Harris County Flood Control District for the Katy-Hockley reservoir, known as Plan 5, below Cypress Creek. Like most of the rivers and streams west of Houston, Cypress Creek flows east towards the bay. Image courtesy of HCFCD.
  • Proposed future development map of roads crisscrossing the Katy Prairie Preserve. Map from page 27 of the Harris County Engineering Dept. US 290 Area Major Thoroughfare Study.

 

A good portion of the land behind the vaguely proposed berm is already under the protection of the Katy Prairie Conservancy, which is “legally, fiscally, and ethically” responsible for it, says Piacentini. For the past twenty-five years the Conservancy has been buying land and creating conservation easements in order to protect and restore native prairie grasslands and wetlands, one of the primary nonstructural or “green” defenses against flooding. The nonprofit organization now has more than 20,000 acres under protection, including 3,000 acres of wetlands as well as working ranchland, and hopes to more than double that. (The source of Buffalo Bayou is in the Katy Prairie.)

But as the Conservancy has been battling to preserve and restore prairie, developers and developer groups like the West Houston Association and Energy Corridor District have been busy developing it as fast as they can. Along with the Sierra Club, the Conservancy has been fighting off plans to put highways and development through the preserve and the prairie, with only partial success. (See Grand Parkway above.)

In the aftermath of the flooding from Harvey, Houston was roundly criticized for carelessly causing its own problems by paving over wetlands and prairie for profit. (See also this pre-Harvey editorial.)

 

An Alternative Solution

Restoring all 21,000 acres of the overflow area to prairie grass and wetland might be another way to handle the water. According to the Conservancy, one acre of wetland can store up to 4.6 acre-feet of water. An acre of tallgrass prairie will temporarily hold 1.2 acre-feet of water. So if one-third of that 21,000 undeveloped (agricultural) land were restored to wetlands, it could theoretically hold 32,000 acre-feet of overflow. And if the remaining 14,000 acres were restored to tallgrass prairie (storing temporarily 16,800 acre-feet of floodwater) the total storage capacity of the natural system would be 48,800 acre-feet, far more than the estimated overflow from Cypress Creek of 23,355 acre-feet during a 100-year event.

According to a 2014 public presentation by HCFCD, the Plan 5 version of the overflow plan would submerge some 11,300 acres of prairie to a depth of eight feet for seven days and produce 26,500 acre-feet of storage – opening some 18,000 acres adjacent to the Grand Parkway for potential development. (p. 43)

“We need to study the details,” says the Conservancy’s Piacentini. “We need to do an analysis of a nature-based project.

“We need to make sure people and structures are not placed in harm’s way.”

 

“As much as I love this house and this setting – It should never have been here.”

The fans were blowing hard inside Michael Huffmaster’s ruined dream home. The soaked first floor, which was built high above the 100-year floodplain, was stripped to the studs. The tall picture windows looked out to the remnant channel of the bayou behind sycamore trees and a dying magnolia. Here and there precious, rescued mementoes were carefully set out to dry: family photographs, a sand-dollar collection, a row of mildewed leather jackets.

“As much as I love this house and this setting – it should never have been here,” said Huffmaster sadly.

[Editorial note: Michelle Foss and Landrum Wise were donors to Save Buffalo Bayou in 2016.]